The recreational pool industry has experienced two dramatic trends that have affected the industry in a pervasive manner. First, the energy crisis has hastened the development of solar energy water-heating apparatus, and today there are numerous solar-energy-based systems which are quite practical and in widespread use in connection with heating pool water. The second recent phenomenon is the widespread popularity of spas or hot tubes, which are installed and used alone or in conjunction with swimming pools.
The energy crisis and the increased interest in and the popularity of spas inherently pose some degree of conflict. Spas normally operate at water temperatures in excess of 90.degree. F. and typically include water jets or the like for circulation of the water and for hydromassage. Both increased water temperature and water circulation require the use of energy. By contrast, however, a spa is a much smaller body of water than a swimming pool, making the total heat required less and the ability to conserve heat by covering the smaller pool of water is more practical.
One area in which efforts to conserve energy have been largely overlooked has been in connection with control apparatus for controlling the operating conditions of the water in a pool system. U.S. Pat. No. 3,991,742 discloses a swimming pool system which employs both a gas heater and a solar heater. The swimming pool filter pump is used to pump water to either the solar heater or the gas heater and subsequently to return the water to the pool. The thrust of U.S. Pat. No. 3,991,742 is directed to the construction of the solar heating apparatus or panels, not a system or apparatus for controlling the flow of pool water as between the solar panels and the gas heater.
In the system of U.S. Pat. No. 3,991,742, the flow of water is controlled by gate valves that are manually operated. In practice most pool water heating systems that include solar and gas heating are either manually controlled or provided with a simple timer that controls a plurality of valves. Thus, the filter pump can be switched off and on by the timer, and the gate valves can be operated by solenoids and coupled to the timer. Such "controlling" of the heaters and other water-conditioning apparatus in recreational pool systems, therefore, has been relatively crude and largely based upon user convenience rather than any attempt at providing energy efficiency.
The control timers which have previously been used with recreational pool systems have also generally been "dumb" controllers in that timing functions proceeded independently and without any feedback as to operating conditions in the pool system or the functioning or failure to function of the other water conditioning apparatus. Mechanical timers will turn on a filter pump and thereby pump pool water into a solar panel located on the roof of a building for a pre-set time period, e.g., four hours, in the middle of the day. If, however, the solar panel has developed a substantial leak, the timer will cause the pump to proceed for four hours to empty the pool by pumping water into the leaking solar panel.
Similarly, when "dumb" controllers are used, one timing function may turn on the gas heater, while another turns on the filter pump. If the filter pump should fail, however, the gas heater will still be operating, with a disastrous effect.
In terms of energy savings, "dumb" timers or controllers can only roughly attempt to achieve some economy in the use of energy. Solar panels can be set to operate during the time of day when solar energy is most likely to be available, filters can be set to function at night when the demand and cost of energy are lowest, and spas can be heated only in the late afternoon and evening, when they are most generally used. Such timing of pool water-conditioning functions, however, only approximates the optimum energy usage for the pool system, and the day-to-day climatic variations which occur will result in a need for constant supervision of the control functions or inefficient energy use, or both.
The ability to truly attain an energy-efficient recreational pool system requires a controller that not only can perform timed sequencing of water-conditioning functions, but can also sense the need for these functions, sense the operation of the equipment during performance of the functions, and preferably, can effect temperature switching as well as timed switching of the water-conditioning functions. Moreover, the ability to sense operation of the pool water-conditioning apparatus and to make control decisions based upon the operation of such apparatus allows the controller to protect the system against "mindless" continued operation that can eventually destroy or endanger the apparatus.
U.S. Pat. No. 3,906,928 discloses a solar-heater control system in which a limited attempt has been made to provide some feedback into a solar pool-heating system. In this patent, a solar-heat sensor is placed proximate the solar panels and is used to control the flow of water to the solar panels. While providing some improvement over a manual or time-switched system, the apparatus and method of U.S. Pat. No. 3,906,928 is relatively simplistic and inherently limited in its control functions.
A somewhat more complex control system for a recreational pool is shown in U.S. Pat. No. 3,809,116. In this system a controller is provided to maintain the liquid level in the pool within a given range. The system includes timed, demand and manual modes of operation, but basically the controller is provided by a relatively simple clock mechanism and a plurality of sensors in the form of switches that will override the clock mechanism. Still further, for most recreational pools the problem of, when to add water, pales by comparison to the water-heating and filtration problems.